The present invention relates to a method for forming a 3D kinematic deformation model of a sedimentary basin from an initial non-deformed state.
Mechanical 3D models of sedimentary basin deformations have already been made. However, these models lead to very complex formulations that have substantial calculating time. An example of such a modeling method is for example described by:
Scott M. et al (1991)  less than  less than Geometrical Modeling of Fault-related Folds: a Pseudo-three-dimensional Approach greater than  greater than ; Journal of Structural Geology, 13, pp.801-812.
Among the existing kinematic models of sedimentary basins, the following models working in 2D can for example be mentioned, described by:
Suppe J.  less than  less than Geometry and Kinematic of Fault-bent Folding greater than  greater than , Am. Journal of Science, 283, pp.684-721 (1993), which does not deal with mechanical compaction, and
Waltham D.  less than  less than Finite Difference Modeling of Sandbox Analogues, Compaction and Detachment Free Deformation greater than  greater than , in Journal of Structural Geology, Vol.12, 3, pp.375-381, 1990, which considers local simple shears but without respecting bank lengths and thicknesses.
French Patent 2,748,516 describes a method for 2D modeling, from a non-deformed initial state, of the evolution of a geologic basin in time by taking account of a) the slip along major tectonic discontinuities with inner deformation of the sediments and of b) the mechanical compaction due to the burial of sediments by tectonic deformation or sedimentation. After preliminary subdivision of the geologic objects of the basin into a certain number of layers or banks, by boundaries (stratigraphic discontinuities defining banks, faults defining imbricate structures, etc.) whose geometrical position is known, the banks are defined by means of grid patterns, the tectonic deformation of each discretized layer is determined separately by respecting as far as possible the thickness and the length thereof, and the grid patterns are modified in order to take account of the compaction associated with the burial variations of the gridded elements. This method is implemented by the FOLDIS(trademark) software.
There are other 2D or  less than  less than pseudo-3D greater than  greater than  models limited to the study of cylindrical symmetry cases or constructed from topologically equivalent 2D sections. An example is described by:
Shaw J. G. et al: Structural Trend Analysis by Axial Surface Mapping; AAPG Bulletin, 78, pp.700-721, 1994.
The method according to the invention forms a (prograde) kinematic model which reproduces in 3D intermediate geometries of geologic objects of an underground zone, from an initial state to a known current state, by interpretation of acquired seismic data, measurements and observations. The method comprises the following steps:
forming a representation of the current geometry of the geologic objects of the zone by interpretation of acquired data obtained by seismic exploration, in-situ measurements and observations;
subdividing each geologic object into superimposed layers, each one of these layers being defined by means of a grid pattern into a series of hexahedral volume elements;
applying separately and successively tectonic deformations to each series of volume elements of a layer in relation to an underlying layer while conserving the thickness and the surface area of an intermediate neutral surface in each volume element; and
modifying iteratively the applied tectonic deformations until a geologic representation substantially in accordance with the known final state of the underground zone is obtained.
By applying thereafter, to a modeling tool of a well-known type, geochemical, thermal or other data associated with intermediate geometries of the geologic objects reproduced by the obtained kinematic model, zones more likely to contain fluids such as hydrocarbons can be readily located or identified in the subsoil.
The method can comprise subdividing each geologic object into layers separated from one another by deformation interfaces (distributed only on the contact surfaces or on intermediate ductile layers).
The method can also comprise a geometrical modification of the grid patterns so as to take into account the effects of compaction.
The modeling method according to the invention, has two parts which are conservation of the surface area of the neutral surface and alternation of rigid layers separated by shear interfaces or ductile interlayers. The model has the advantage of being easy to implement, coherently reproduces the inner deformations undergone by the layers and better represents the shear that can be observed between two rigid layers, even in cases of complex structures.
The model obtained with the method of the invention allows reconstruction of a geologically acceptable deformation course. All the intermediate geometries of the evolution process followed by the sedimentary basin are reproduced incrementally in time.
This type of basin model is an invaluable tool for geologists which allows showing permeability variation, the expulsion of fluids by compaction, the calculation of thermal transfers in the basin, the maturation of the organic matter and the circulation of the fluids, and facilitates defining hydrocarbon accumulation zones and the most favorable conditions for developing them.